As well known to those skilled in the art, when making a box, a soft sheet such as paper, synthetic resin and the like, is initially cut through blanking and piercing processes to prepare an initial sheet product. The initial sheet product is tailored to a developed state of the box, and then, by folding and bonding the tailored sheet product, formation of the box is completed.
In the tailoring procedure which is initially implemented when making the box, a cutting blade formed to have a configuration corresponding to the developed state of the box is installed on a cutting blade holder which has a plate-shaped contour, so that a cutting edge of the cutting blade projects downward. The cutting blade holder is mounted to a ram of a press. In a state wherein many folds of sheets are placed on a die, by lowering and then raising the ram, the sheets are tailored into the desired configuration by the cutting blade.
The cutting blade is formed of a special steel having a thin band-shaped contour, the cutting edge is formed at one widthwise end of the cutting blade to extend in a lengthwise direction of the cutting blade. The conventional procedure for fabricating the cutting blade comprises the steps of forming the cutting edge by grinding one widthwise end of the blade, defining a bending groove or a bridging groove, and conducting bending and severing processes.
In connection with fabrication of a cutting blade, a bending process can be implemented as disclosed in Japanese Patent Laid-open Publication Gazette No. Heisei 8-99123. That is to say, the cutting blade is bent leftward or rightward in conformity with a size of a desired configuration under the control of a computer program. Concretely speaking, by finely moving in a controlled manner a movable bending member which is positioned at a distal end of a guide member, the cutting blade which is discharged in a fitted state by the guide member is properly bent.
However, in the Japanese Patent Laid-open Publication Gazette, when implementing the cutting blade fabricating procedure, for example, when it is necessary to bend the cutting blade at the right angle, over an area where the bending of the cutting blade takes place, since a compression stress is produced in an inner part of the cutting blade and a tensile stress is produced in an outer part of the cutting blade, a round of a certain radius is formed. Thus, it is difficult to bend the cutting blade at an accurate right-angle.
In other words, when bending the cutting blade, due to a characteristic of a metallic material, because the cutting blade is bent while forming the round of a certain radius, it is difficult to precisely bend the cutting blade at a desired angle. As a consequence, a problem is caused in that a fabrication error of a certain extent cannot but be accepted.
Therefore, when conducting a bending process of a cutting blade, particular attention must be paid to define a precise bending angle while not forming a round.
In this consideration, in Korean Utility Model Registration No. 155939 which is registered in the name of the present applicant, a cutting blade is formed using a thin band of a predetermined width, and a cutting edge is formed at one widthwise end of the cutting blade. In order to ensure that the cutting blade can be bent by a predetermined angle at a desired position to have the same configuration as a product to be cut, a groove is defined in the cutting blade to extend in a widthwise direction of the cutting blade. Hence, it is possible to bend at the desired position the cutting blade to various angles including a right angle and an acute angle, while not causing the formation of a round having a certain radius. It is illustrated that the bending groove is defined as a grinder or a bite (cutting tool) is lowered by a cylinder.
Nevertheless, in the case that the bending groove of the cutting blade is defined using the grinder, as the wear of a grinding stone proceeds, a sectional shape of the bending groove may be changed. Also, in the case that the bending groove of the cutting groove is defined using the bite, after the bending groove is defined, when the bite is returned to its initial position, since the bite is not retreated and returned in a direction opposite to its machining direction, the bite is raised in a state wherein it is brought into contact with the cutting blade. Due to contact between the bite and the cutting blade, frictional heat is generated to cause degradation of the bite.
Specifically, when defining the groove using the grinder or bite, since there is not provided a separate structure for supporting a machining area of the cutting blade, a bending phenomenon occurs in the cutting blade, whereby it is difficult to precisely define the groove in the cutting blade.
In Korean Patent No. 239943, there is disclosed an apparatus in which arc-shaped grooves for enabling bending of a cutting blade are defined on upper and lower surfaces of the cutting blade using grinding rolls which are rotated about a horizontal shaft.
In this apparatus, while the grinding rolls having a minimum length corresponding to a width of the cutting blade press the upper and lower surfaces of the cutting blade to define the bending grooves, since there is not provided a separate structure for supporting a machining area of the cutting blade, the machining area of the cutting blade is likely to be defined during machining, whereby it is difficult to precisely define the grooves in the cutting blade.
Further, in the case that the cutting blade is formed to have a T-shaped section, a quadrangular groove cannot be precisely defined at a predetermined position. Because it is difficult to grind one end of the cutting blade to have a semicircular sectional shape, a cutting blade portion cannot be precisely fixed to the cutting blade.